```html
<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>算法之美：验证回文串</title>
    <link href="https://cdn.staticfile.org/font-awesome/6.4.0/css/all.min.css" rel="stylesheet">
    <link href="https://cdn.staticfile.org/tailwindcss/2.2.19/tailwind.min.css" rel="stylesheet">
    <link href="https://fonts.googleapis.com/css2?family=Noto+Serif+SC:wght@400;500;600;700&family=Noto+Sans+SC:wght@300;400;500;700&display=swap" rel="stylesheet">
    <script src="https://cdn.jsdelivr.net/npm/mermaid@latest/dist/mermaid.min.js"></script>
    <style>
        body {
            font-family: 'Noto Sans SC', Tahoma, Arial, Roboto, "Droid Sans", "Helvetica Neue", "Droid Sans Fallback", "Heiti SC", "Hiragino Sans GB", Simsun, sans-serif;
            background-color: #f8fafc;
            color: #1e293b;
        }
        .hero-gradient {
            background: linear-gradient(135deg, #3b82f6 0%, #6366f1 100%);
        }
        .code-block {
            background-color: #1e293b;
            color: #e2e8f0;
            border-left: 4px solid #3b82f6;
        }
        .card-hover {
            transition: all 0.3s ease;
        }
        .card-hover:hover {
            transform: translateY(-5px);
            box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
        }
        .first-letter {
            font-size: 3.5rem;
            line-height: 1;
            float: left;
            margin-right: 0.5rem;
            margin-top: 0.2rem;
            color: #3b82f6;
            font-weight: 700;
        }
    </style>
</head>
<body>
    <div class="min-h-screen">
        <!-- Hero Section -->
        <section class="hero-gradient text-white py-20 px-4 sm:px-6 lg:px-8">
            <div class="max-w-5xl mx-auto">
                <h1 class="text-4xl sm:text-5xl lg:text-6xl font-bold mb-6 font-serif">验证回文串</h1>
                <p class="text-xl sm:text-2xl text-blue-100 max-w-3xl leading-relaxed">
                    探索算法之美，从对称中寻找效率的平衡点
                </p>
                <div class="mt-10 flex items-center space-x-4">
                    <span class="px-4 py-2 bg-white bg-opacity-20 rounded-full text-sm font-medium">双指针</span>
                    <span class="px-4 py-2 bg-white bg-opacity-20 rounded-full text-sm font-medium">时间复杂度 O(n)</span>
                </div>
            </div>
        </section>

        <!-- Main Content -->
        <main class="max-w-5xl mx-auto px-4 sm:px-6 lg:px-8 py-16">
            <!-- Problem Description -->
            <section class="mb-16">
                <div class="flex items-center mb-8">
                    <div class="w-12 h-12 rounded-full bg-blue-100 flex items-center justify-center mr-4">
                        <i class="fas fa-question-circle text-blue-600 text-xl"></i>
                    </div>
                    <h2 class="text-2xl font-bold text-slate-800">题目描述</h2>
                </div>
                <div class="bg-white rounded-xl shadow-md p-6">
                    <p class="text-lg leading-relaxed">
                        给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，忽略字母的大小写。
                    </p>
                </div>
            </section>

            <!-- Algorithm Visualization -->
            <section class="mb-16">
                <div class="flex items-center mb-8">
                    <div class="w-12 h-12 rounded-full bg-blue-100 flex items-center justify-center mr-4">
                        <i class="fas fa-project-diagram text-blue-600 text-xl"></i>
                    </div>
                    <h2 class="text-2xl font-bold text-slate-800">算法可视化</h2>
                </div>
                <div class="bg-white rounded-xl shadow-md p-6">
                    <div class="mermaid">
                        graph LR
                        A[开始] --> B[初始化左右指针]
                        B --> C{左 < 右?}
                        C -->|是| D[跳过非字母数字字符]
                        D --> E{字符匹配?}
                        E -->|否| F[返回False]
                        E -->|是| G[移动指针]
                        G --> C
                        C -->|否| H[返回True]
                        F --> I[结束]
                        H --> I
                    </div>
                </div>
            </section>

            <!-- Solution -->
            <section class="mb-16">
                <div class="flex items-center mb-8">
                    <div class="w-12 h-12 rounded-full bg-blue-100 flex items-center justify-center mr-4">
                        <i class="fas fa-lightbulb text-blue-600 text-xl"></i>
                    </div>
                    <h2 class="text-2xl font-bold text-slate-800">解题思路</h2>
                </div>
                <div class="bg-white rounded-xl shadow-md overflow-hidden">
                    <div class="p-6">
                        <div class="mb-6">
                            <span class="first-letter">双</span>
                            <p class="text-lg leading-relaxed">
                                指针技术是解决回文串问题的经典方法。使用两个指针分别从字符串的开头和结尾向中间移动，跳过非字母数字字符，比较两个指针指向的字符是否相同。
                            </p>
                        </div>
                        <div class="grid md:grid-cols-2 gap-6">
                            <div class="bg-slate-50 p-6 rounded-lg border border-slate-200">
                                <div class="flex items-center mb-3">
                                    <i class="fas fa-clock text-blue-500 mr-2"></i>
                                    <h3 class="font-medium text-slate-800">时间复杂度</h3>
                                </div>
                                <p class="text-slate-600">O(n) - 只需遍历字符串一次</p>
                            </div>
                            <div class="bg-slate-50 p-6 rounded-lg border border-slate-200">
                                <div class="flex items-center mb-3">
                                    <i class="fas fa-memory text-blue-500 mr-2"></i>
                                    <h3 class="font-medium text-slate-800">空间复杂度</h3>
                                </div>
                                <p class="text-slate-600">O(1) - 仅使用固定大小的额外空间</p>
                            </div>
                        </div>
                    </div>
                    <div class="bg-slate-800 text-white p-6">
                        <div class="flex items-center mb-4">
                            <i class="fas fa-code text-blue-400 mr-2"></i>
                            <h3 class="font-medium">示例代码</h3>
                        </div>
                        <pre class="code-block p-4 rounded-lg overflow-x-auto"><code class="text-sm">def isPalindrome(s):
    left, right = 0, len(s) - 1
    while left < right:
        while left < right and not s[left].isalnum():
            left += 1
        while left < right and not s[right].isalnum():
            right -= 1
        if s[left].lower() != s[right].lower():
            return False
        left += 1
        right -= 1
    return True</code></pre>
                    </div>
                </div>
            </section>

            <!-- Execution Process -->
            <section class="mb-16">
                <div class="flex items-center mb-8">
                    <div class="w-12 h-12 rounded-full bg-blue-100 flex items-center justify-center mr-4">
                        <i class="fas fa-play-circle text-blue-600 text-xl"></i>
                    </div>
                    <h2 class="text-2xl font-bold text-slate-800">执行过程演示</h2>
                </div>
                <div class="bg-white rounded-xl shadow-md p-6">
                    <div class="mermaid">
                        sequenceDiagram
                        participant 左指针
                        participant 字符串
                        participant 右指针
                        左指针->>字符串: 初始位置 0
                        右指针->>字符串: 初始位置 len(s)-1
                        loop while 左 < 右
                            左指针->>字符串: 跳过非字母数字字符
                            右指针->>字符串: 跳过非字母数字字符
                            alt 字符不匹配
                                左指针->>字符串: 返回 False
                            else 字符匹配
                                左指针->>字符串: 向右移动
                                右指针->>字符串: 向左移动
                            end
                        end
                        左指针->>字符串: 返回 True
                    </div>
                </div>
            </section>

            <!-- Key Points -->
            <section>
                <div class="flex items-center mb-8">
                    <div class="w-12 h-12 rounded-full bg-blue-100 flex items-center justify-center mr-4">
                        <i class="fas fa-key text-blue-600 text-xl"></i>
                    </div>
                    <h2 class="text-2xl font-bold text-slate-800">关键要点</h2>
                </div>
                <div class="grid md:grid-cols-2 gap-6">
                    <div class="bg-white rounded-xl shadow-md p-6 card-hover">
                        <div class="flex items-center mb-4">
                            <div class="w-10 h-10 rounded-full bg-blue-50 flex items-center justify-center mr-3">
                                <i class="fas fa-filter text-blue-500"></i>
                            </div>
                            <h3 class="font-medium text-lg">字符过滤</h3>
                        </div>
                        <p class="text-slate-600">使用 isalnum() 方法过滤掉非字母数字字符，确保只比较有效字符。</p>
                    </div>
                    <div class="bg-white rounded-xl shadow-md p-6 card-hover">
                        <div class="flex items-center mb-4">
                            <div class="w-10 h-10 rounded-full bg-blue-50 flex items-center justify-center mr-3">
                                <i class="fas fa-arrows-alt-h text-blue-500"></i>
                            </div>
                            <h3 class="font-medium text-lg">双指针移动</h3>
                        </div>
                        <p class="text-slate-600">左右指针从两端向中间移动，相遇时完成验证，确保高效性。</p>
                    </div>
                    <div class="bg-white rounded-xl shadow-md p-6 card-hover">
                        <div class="flex items-center mb-4">
                            <div class="w-10 h-10 rounded-full bg-blue-50 flex items-center justify-center mr-3">
                                <i class="fas fa-exchange-alt text-blue-500"></i>
                            </div>
                            <h3 class="font-medium text-lg">大小写忽略</h3>
                        </div>
                        <p class="text-slate-600">统一转换为小写或大写进行比较，解决大小写敏感问题。</p>
                    </div>
                    <div class="bg-white rounded-xl shadow-md p-6 card-hover">
                        <div class="flex items-center mb-4">
                            <div class="w-10 h-10 rounded-full bg-blue-50 flex items-center justify-center mr-3">
                                <i class="fas fa-check-circle text-blue-500"></i>
                            </div>
                            <h3 class="font-medium text-lg">边界处理</h3>
                        </div>
                        <p class="text-slate-600">正确处理空字符串和全为特殊字符的边界情况。</p>
                    </div>
                </div>
            </section>
        </main>
    </div>

    <script>
        mermaid.initialize({
            startOnLoad: true,
            theme: 'default',
            flowchart: {
                useMaxWidth: false,
                htmlLabels: true,
                curve: 'basis'
            },
            sequence: {
                diagramMarginX: 50,
                diagramMarginY: 10,
                actorMargin: 50,
                width: 200,
                height: 30,
                boxMargin: 10,
                boxTextMargin: 5,
                noteMargin: 10,
                messageMargin: 35,
                mirrorActors: false,
                bottomMarginAdj: 1,
                useMaxWidth: false
            }
        });
    </script>
</body>
</html>
```